1. Field of the Invention
The present invention relates to joysticks and, more particularly, relates to joysticks for electronically actuated proportional valves which control heavy industrial equipment.
2. Description of the Related Art
A wide variety of industrial devices and vehicles employ electronically actuated proportional valves to perform functions of the devices. Such valves may directly control the operation of a device such as a hydraulic piston and cylinder arrangement. Such valves may also indirectly control the operation of a device such as a hydrostatic transmission. Many such valves have two or more coils permitting the valves to be positioned in any activation state.
These industrial valves are typically actuated by moving a joystick through one of a plurality of axes. The typical joystick includes a pivotable lever coupled to a potentiometer which generates an output signal representative of the position and/or rate of motion of the joystick. The output of the potentiometer is in turn transmitted to the coil of a servo or solenoid valve to actuate the valve. Joysticks employing potentiometers to detect the operational state of the joystick lever exhibit several disadvantages. For instance, such potentiometers, while varying greatly in construction, all utilize the direct interface of a stationary conductor and a movable wiper in electrical contact with one another. These potentiometers are subject to rapid wear when used in environments that undergo high vibration such as that found on mobile equipment such as cranes. More specifically, the potentiometer wipers will continuously reciprocate through a small distance due to the vibration of the device on which it is mounted. This movement quickly degrades or wipes off the lubricant between the stationary element and the wiper, leading to relatively rapid wear and failure of the potentiometer and thus of the joystick. Even so called "non-lubricated" plastic resistive element-type potentiometers will incur this type of failure. Signal generators employing potentiometers also employ relatively complex drive systems incorporating various gears, cam followers, etc. Such mechanisms are relatively bulky, expensive and difficult to assemble, and prone to failure.
Some of the problems associated with potentiometer-type detection circuits can be eliminated through the provision of so-called "contactless" sensors. These sensors do not require direct electrical contact between the actuating lever and the signal generator and thus are not as prone to failure.
One such contactless position detector comprises a so-called "inductively coupled" position detector, otherwise known as a "linear induction sensor". The typical inductively coupled position detector employs a transmitting or drive coil positioned on the end of the joystick lever and a plurality of pickup or sensor coils which are positioned proximate the transmitting coil and which generate an electrical signal when a transmitting coil moves into the proximity of one of the respective pickup coils. These signals are transmitted to a circuit board and combined so as to provide a signal indicative of the position of the joystick.
While contactless detection systems such as inductively coupled position detectors avoid many of the problems associated with the use of potentiometer-type detectors, these detectors do not generate a current of a sufficient magnitude to actuate electrically operated proportional valves and thus require the provision of valve drivers which receive the signals generated b the position detector and which generate an electric current of sufficient magnitude to actuate a valve. These valve drivers are typically provided on circuit boards and are sometimes known as drive boards.
Heretofore, valve drivers have been provided as modular units at a location between the joystick and the valves to be actuated. Such externally positioned valve drivers exhibit several disadvantages.
For instance, systems employing separate modular joysticks and valve drivers are relatively bulky and require independent mounting of the joystick and valve driver modules. The valve driver modules are often placed in a location which is open to the elements, and are thus subject to damage through crushing, water damage, etc.
Valve drivers located remote from the position detector are also prone to interference because the relatively long electrical connections joining these elements tend to act as antennas which pick up electrical interference signals. These connections are also exposed to the elements and are thus prone to breakage.
Moreover, it is often necessary to adjust the operational parameters of the valve driver to meet a particular application. For instance, it may be necessary to set the maximum voltage level for full joystick displacement or to set a designated voltage increase rate or ramp rate for a particular application. Such adjustments are most easily performed during operation of the joystick. However, if the valve driver is located remote from the joystick, such simultaneous adjustments cannot be performed by a single operator. It is therefore necessary to employ a first operator to operate the joystick and another operator to adjust the valve driver. Similarly, although some systems employ diagnostic visual indications of the status of the system, such indicators are not mounted on the joystick and thus may not be positioned in a location which can be easily viewed by the user while operating the joystick.
The typical joystick also is incapable of responding to a signal wire failure or to a joystick fault in which the valve being controlled is not completely de-energized when the joystick is in its neutral position. Failure of a system to respond to either of these conditions is potentially hazardous because it may lead to unintended partial or complete actuation of a valve and of the implement being controlled by the valve.